To transition from the current energy economy, based on the consumption of nonrenewable petroleum-based energy sources, into a future energy economy, in which humans sustainably produce, store, and consume renewable energy, a series of technological challenges must be met. With respect to automotive transportation, in particular, first and foremost among these challenges is the unmet need for renewable energy storage devices which are suitable replacements for the internal combustion engine. Rechargeable batteries and lithium (Li) rechargeable batteries, in particular, are useful substitutes in some automotive applications, such as all electric and hybrid-electric vehicles, but the high cost and limited performance of conventional rechargeable batteries remains the main impediment preventing mainstream adoption of electric vehicle technology. Solid state rechargeable batteries have been proposed as next generation batteries for automotive applications in large part due to the increased energy density (volumetric and gravimetric) possible for these batteries when compared to their conventional liquid-electrolyte based. Of these solid state batteries, those which include a lithium metal anode are thought to achieve the highest energy densities due to the maximized difference in voltage for a Li ion situated in any cathode active material relative to Li in Li metal.
In a rechargeable Li ion battery, Li+ ions move from a negative electrode to a positive electrode during discharge of the battery and in the opposite direction during charge. An electrolyte separates and electrically insulates the positive and negative electrodes while also providing a conduit for Li+ ions to conduct between the electrodes. The electrolyte also ensures that the electrons, which are produced at the same time that Li+ ions (e.g., Li⇄Li++e−) are produced during discharge of battery, are conducted by way of a pathway which is external and parallel to the Li+ ion conduction pathway. A critically important component of solid state batteries is therefore the electrolyte, which electrically isolates the positive and negative electrodes, and a catholyte, which is intimately mixed with a positive electrode active material to facilitate the ionic conductivity therein. A third important component, in some Li ion batteries, is an anolyte which is laminated to, or in contact with, an anode material (i.e., negative electrode material; e.g., Li-metal) and which may provide a chemically stable barrier between the anode material on one side of the anolyte and the solid-state electrolyte on the other side of the anolyte. Currently available electrolyte, catholyte, and anolyte materials, however, are not sufficiently stable within, or otherwise suitable for use with, solid state batteries which include Li metal anodes or which operate above 4.2V.
Conventional rechargeable batteries use liquid-based electrolytes which include lithium salts in organic solvents (e.g., 1M LiPF6 in 1:1 ethylene carbonate:diethylene carbonate). However, these electrolytes suffer from several problems including outgassing at high voltage and flammability of the organic solvents during thermal runaway (short circuit, e.g., Li-dendrite). As an alternative to these liquid-based electrolytes, Li batteries with a solid-state sulfide-based electrolyte membrane have been described. For example, certain sulfide-based electrolyte materials have been known as solid-state electrolytes suitable for use in solid-state lithium battery. See, for example, (a) S. Ujiie, et al., Solid State Ionics, 211 (2012) 42-45; (b) S. Ujiie, et al., J Solid State Electrochem., (2013) 17:675-680; (c) Hans-Jorg Deiseroth, et al., Angew. Chem. Int. Ed., 2008, 47, 755-758; (d) Prasada Rao Rayavarapu, et al., J Solid State Electrochem., (2012) 16:1807-1813; (e) Shiao-Tong Kong, Chem. Eur. J. 2010, 16, 2198-2206; (f) Ezhiylmurugan Rangasamy, et al., DOI: 10.1021/ja508723m; (g) Kato, Y. et al., Nature Energy, Article number 16030 (2016) doi:10.1038/nenergy.2016.30. Some publications, such as U.S. Pat. No. 7,390,591 to Visco, et al., set forth layered solid-state sulfide-based electrolytes which include one layer which is a Li-metal-interfacing and lithium-metal-compatible layer (e.g., Li3N, Li3P, LiI, LiBr, LiCl, LiF and LiPON) and which is laminated to a second layer which is a cathode-interfacing and cathode-compatible-layer which may include a sulfide-based electrolyte (e.g., Li3PO4.Li2S.SiS2, Li2S.GeS2.Ga2S3). Such solid-state electrolytes suffer, however, from poor conductivity and chemical instability such that they are not suitable for large scale market adoption in solid-state batteries which include a Li metal anode. As such, there exists a need for improved solid-state sulfide-based electrolytes and catholytes. The instant disclosure sets forth such electrolytes and catholytes, as well as methods for making and using the same.